dnsop W. Kumari
Internet-Draft Google
Intended status: Informational A. Sullivan
Expires: July 22, 2018 Oracle
January 18, 2018
The ALT Special Use Top Level Domain
draft-ietf-dnsop-alt-tld-09
Abstract
This document reserves a string (ALT) to be used as a TLD label in
non-DNS contexts. It also provides advice and guidance to developers
developing alternative namespaces.
[Ed note: Text inside square brackets ([]) is additional background
information, answers to frequently asked questions, general musings,
etc. They will be removed before publication. This document is
being collaborated on in Github at: https://github.com/wkumari/draft-
wkumari-dnsop-alt-tld. The most recent version of the document, open
issues, etc should all be available here. The authors (gratefully)
accept pull requests. ]
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 22, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 2
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The ALT namespace . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Choice of the ALT Name . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
4.1. Domain Name Reservation Considerations . . . . . . . . . 5
5. Privacy Considerations . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Many protocols and systems need to name entities. Names that look
like DNS names (a series of labels separated with dots) have become
common, even in systems that are not part of the global DNS
administered by IANA. This document reserves the label "ALT" (short
for "Alternative") as a Special Use Domain ([RFC6761]). This label
is intended to be used as the final (rightmost) label to signify that
the name is not rooted in the DNS, and that it should not be resolved
using the DNS protocol.
1.1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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1.2. Terminology
This document assumes familiarity with DNS terms and concepts.
Please see [RFC1034] for background and concepts, and [RFC7719] for
terminology. Readers are also expected to be familiar with the
discussions in [I-D.ietf-dnsop-sutld-ps]
o DNS name: Domain names that are intended to be used with DNS
resolution, either in the global DNS or in some other context
o DNS context: The namespace anchored at the globally-unique DNS
root. This is the namespace or context that "normal" DNS uses.
o non-DNS context: Any other (alternative) namespace.
o pseudo-TLD: A label that appears in a fully-qualified domain name
in the position of a TLD, but which is not registered in the
global DNS. This term is not intended to be pejorative.
o TLD: The last visible label in either a fully-qualified domain
name or a name that is qualified relative to the root. See the
discussion in Section 2.
2. Background
The success of the DNS makes it a natural starting point for systems
that need to name entities in a non-DNS context.
In many cases, these systems build a DNS-style tree parallel to, but
separate from, the global DNS. They often use a pseudo-TLD to cause
resolution in the alternative namespace, using browser plugins, shims
in the name resolution process, or simply applications that perform
special handling of this particular alternative namespace. An
example of such a system is the Tor network's [Dingledine2004] use of
the ".onion" Special-Use Top-Level Domain Name (see [RFC7686]).
In many cases, the creators of these alternative namespaces have
chosen a convenient or descriptive string and started using it.
These strings are not registered anywhere nor are they part of the
DNS. However, to users and to some applications, they appear to be
TLDs; and issues may arise if they are looked up in the DNS. This
document suggests that name resolution libraries (stub resolvers)
recognize names ending in ".alt" as special, and not attempt to look
them up using the DNS protocol in order to limit the effects of
queries accidentally leaking into the DNS.
The techniques in this document are primarily intended to address the
"Experimental Squatting Problem", the "Land Rush Problem" and "Name
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Collisions" issues discussed in [I-D.ietf-dnsop-sutld-ps] (which
contains much additional background, etc).
3. The ALT namespace
This document reserves the ALT label, using the [RFC6761] process,
for use as an unmanaged pseudo-TLD namespace. The ALT label MAY be
used in any domain name as a pseudo-TLD to signify that this is an
alternative (non-DNS) namespace, and should not be looked up in a DNS
context.
Alternative namespaces should differentiate themselves from other
alternative namespaces by choosing a name and using it in the label
position just before the pseudo-TLD (ALT). For example, a group
wishing to create a namespace for Friends Of Olaf might choose the
string "foo" and use any set of labels under foo.alt.
As names beneath ALT are in an alternative namespace, they have no
significance in the regular DNS context and so should not be looked
up in the DNS context.
Groups wishing to create new alternative namespaces may create their
alternative namespace under a label that names their namespace under
the ALT label. They should attempt to choose a label that they
expect to be unique and, ideally, descriptive. There is no IANA
registry for names under the ALT TLD - it is an unmanaged namespace,
and developers are responsible for dealing with any collisions that
may occur under .alt. Informal lists of namespaces under .alt may be
created to assist the developer community.
Currently deployed projects and protocols that are using pseudo-TLDs
may choose to move under the ALT TLD, but this is not a requirement.
Rather, the ALT TLD is being reserved so that current and future
projects of a similar nature have a designated place to create
alternative resolution namespaces that will not conflict with the
regular DNS context.
3.1. Choice of the ALT Name
A number of names other than "ALT" were considered and discarded.
While these are not DNS names, in order for this technique to be
effective the names need to continue to follow both the DNS format
and conventions (a prime consideration for alternative name formats
is that they can be entered in places that normally take DNS context
names); this rules out using suffixes that do not follow the usual
letter, digit, and hyphen label convention.
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A short label was deemed desirable for a number of reasons,
including:
o this is a switch to other resolution contexts, some which may have
long labels (for example derived from public keys).
o some queries will undoubtedly leak into the DNS. As many of these
alternate resolution systems are specifically designed for
privacy, limiting how far they leak is desirable.
o as there are not protocol police, the label needs to be attractive
to implementors of alternate resolution contexts so that they are
willing to use this.
4. IANA Considerations
The IANA is requested to add the ALT string to the "Special-Use
Domain Name" registry ([RFC6761], and reference this document.
4.1. Domain Name Reservation Considerations
This section is to satisfy the requirement in Section 5 of RFC6761.
The string ".alt." (and names ending with the string .alt) are
special in the following ways:
1. Users are expected to know that strings that end in .alt behave
differently to normal DNS names. Users are expected to have
applications running on their machines that intercept strings of
the form .alt and perform special handing of them, or
that applications themselves will recognize the strings as
special, and perform special handling. If the user tries to
resolve a name of the form .alt without the
plugin installed (or in the wrong application), the
request will leak into the DNS, receive a negative response, and
the resolution will fail.
2. Writers of application software that implement a non-DNS
namespace are expected to intercept names of the form
.alt and perform application specific handing with
them. Other applications are not required to perform any special
handing (but may choose to provide helpful informational messages
if able).
3. Writers of name resolution APIs and libraries which operate in
the DNS context should not attempt to look these names up in the
DNS. If developers of other namespaces implement their namespace
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through a "shim" or library, they will need to intercept and
perform their own handling.
4. Caching DNS servers SHOULD NOT recognize these names as special
and should not perform any special handling with them.
5. Authoritative DNS servers SHOULD NOT recognize these names as
special and should not perform any special handling with them.
6. DNS server operators SHOULD be aware that queries for names
ending in .alt are not DNS names, and were leaked into the DNS
context (for example, by a missing browser plugin). This
information may be useful for support or debugging purposes.
7. DNS Registries/Registrars MUST NOT grant requests to register
".alt" names in the normal way to any person or entity. These
".alt" names are defined by protocol specification to be
nonexistent, and they fall outside the set of names available for
allocation by registries/registrars.
Earlier versions of this document requested that .ALT be added to the
"Locally Served Zones" registry, and that a DNSSEC insecure
delegation (a delegation with no DS record) be created at the root.
Significant discussion on the DNSOP list (and an interim meeting)
generated the consensus that these names are specifically not DNS
names, and that them leaking into the DNS is an error. This means
that the current (non-delegated) response of NXDOMAIN is correct as
there is no DNS domain .alt, and so the document was updated to
remove these requests.
5. Privacy Considerations
This document reserves ALT to be used to indicate that a name is not
a DNS name, and so should not attempt to be resolved using the DNS.
Unfortunately, these queries will undoubtedly leak into the DNS - for
example, a user may receive an email containing a hostname which
should be resolved using a specific resolution context (implemented
by a specific application or resolution mechanism). If the user does
not have that particular application installed (and their stub
resolver library has not been updated to ignore queries for names
ending in .alt), it is likely that this will instead be resolved
using the DNS. This DNS query will likely be sent to the configured
iterative resolver. If this resolver does not have a cache entry for
this name (or, if the resolver implements
[I-D.ietf-dnsop-nsec-aggressiveuse], a entry for .alt) this query
will likely be sent to the DNS root servers. This exposes the
(leaked) query name to the operator of the resolver, the operator of
the queried DNS root server, and anyone watching queries along the
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path. This is a general problem with alternative name spaces and not
confined to names ending in .alt.
6. Security Considerations
One of the motivations for the creation of the .alt pseudo-TLD is
that unmanaged labels in the managed root name space are subject to
unexpected takeover. This could occur if the manager of the root
name space decides to delegate the unmanaged label.
The unmanaged and "registration not required" nature of labels
beneath .alt provides the opportunity for an attacker to re-use the
chosen label and thereby possibly compromise applications dependent
on the special host name.
7. Acknowledgements
We would like to thank Joe Abley, Mark Andrews, Marc Blanchet, John
Bond, Stephane Bortzmeyer, David Cake, David Conrad, Steve Crocker,
Brian Dickson, Ralph Droms, Robert Edmonds, Patrik Faltstrom, Olafur
Gudmundsson, Bob Harold, Paul Hoffman, Joel Jaeggli, Ted Lemon,
Edward Lewis, John Levine, George Michaelson, Ed Pascoe, Jim Reid,
Arturo Servin, Paul Vixie, Suzanne Woolf for feedback.
Christian Grothoff was also very helpful.
8. References
8.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997, .
[RFC6303] Andrews, M., "Locally Served DNS Zones", BCP 163, RFC
6303, DOI 10.17487/RFC6303, July 2011, .
[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, DOI 10.17487/RFC6761, February 2013,
.
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[RFC7686] Appelbaum, J. and A. Muffett, "The ".onion" Special-Use
Domain Name", RFC 7686, DOI 10.17487/RFC7686, October
2015, .
[RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", RFC 7719, DOI 10.17487/RFC7719, December
2015, .
8.2. Informative References
[Dingledine2004]
Dingledine, R., Mathewson, N., and P. Syverson, "Tor: The
Second-Generation Onion Router", , 8 2004,
<>.
[I-D.ietf-dnsop-nsec-aggressiveuse]
Fujiwara, K., Kato, A., and W. Kumari, "Aggressive use of
DNSSEC-validated Cache", draft-ietf-dnsop-nsec-
aggressiveuse-10 (work in progress), May 2017.
[I-D.ietf-dnsop-sutld-ps]
Lemon, T., Droms, R., and W. Kumari, "Special-Use Domain
Names Problem Statement", draft-ietf-dnsop-sutld-ps-08
(work in progress), August 2017.
Appendix A. Changes / Author Notes.
[RFC Editor: Please remove this section before publication ]
From -07 to -08:
o Made it clear that this is only for non-DNS.
o As per Interim consensus, removed the "add this to local zones"
text.
o Added a Privacy Considerations section
o Grammar fix -- "alternative" is more correct than "alternate",
replaced.
From -06 to -07:
o Rolled up the GItHub releases in to a full release.
From -07.2 to -07.3 (GitHub point release):
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Removed 'sandbox' at Stephane's suggestion - https://www.ietf.org/
mail-archive/web/dnsop/current/msg18495.html
Suggested (in 4.1 bullet 3) that DNS libraries ignore these -- Bob
Harold - https://mailarchive.ietf.org/arch/msg/dnsop/
a_ruPf8osSzi_hCzCqOxYLXhYoA
Added some pointers to the SUTLD document.
From -07.1 to -07.2 (Github point release):
o Reverted the string (at request of chairs).
o Added an editors note explaining the above.
o Removed some more background, editorializing, etc.
From -06 to -07.1 (https://github.com/wkumari/draft-wkumari-dnsop-
alt-tld/tree/7988fcf06100f7a17f21e6993b781690b5774472):
o Replaced ALT with at the suggestions of George.
From -05 to -06:
o Removed a large amount of background - we now have the (adopted)
tldr document for that.
o Made it clear that pseudo-TLD is not intended to be pejorative.
o Tried to make it cleat that this is something people can choose to
use - or not.
From -04 to -05:
o Version bump - we are waiting in the queue for progress on SUN,
bumping this to keep it alive.
From -03 to -04:
o 3 changes - the day, the month and the year (a bump to keep
alive).
From -02 to -03:
o Incorporate suggestions from Stephane and Paul Hoffman.
From -01 to -02:
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o Merged a bunch of changes from Paul Hoffman. Thanks for sending a
git pull.
From -00 to 01:
o Removed the "delegated to new style AS112 servers" text -this was
legacy from the omnicient AS112 days. (Joe Abley)
o Removed the "Advice to implemntors" section. This used to
recommend that people used a subdomain of a domain in the DNS. It
was pointed out that this breaks things badly if the domain
expires.
o Added text about why we don't want to adminster a registry for
ALT.
From Individual-06 to DNSOP-00
o Nothing changed, simply renamed draft-wkumari-dnsop-alt-tld to
draft-ietf-dnsop-alt-tld
From -05 to -06
o Incorporated comments from a number of people, including a number
of suggestion heard at the IETF meeting in Dallas, and the DNSOP
Interim meeting in May, 2015.
o Removed the "Let's have an (optional) IANA registry for people to
(opportinistically) register their string, if they want that
option" stuff. It was, um, optional....
From -04 to -05
o Went through and made sure that I'd captured the feedback
received.
o Comments from Ed Lewis.
o Filled in the "Domain Name Reservation Considerations" section of
RFC6761.
o Removed examples from .Onion.
From -03 to -04
o Incorporated some comments from Paul Hoffman
From -02 to -03
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o After discussions with chairs, made this much more generic (not
purely non-DNS), and some cleanup.
From -01 to -02
o Removed some fluffy wording, tightened up the language some.
From -00 to -01.
o Fixed the abstract.
o Recommended that folk root their non-DNS namespace under a DNS
namespace that they control (Joe Abley)
Authors' Addresses
Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: warren@kumari.net
Andrew Sullivan
Oracle
150 Dow Street
Manchester, NH 03101
US
Email: asullivan@dyn.com
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